DE3507618A1 - Method for token-error correction in a token-ring telecommunications system - Google Patents

Abstract

In a single-token ring system, every transmitting station interrupts the transmission of information packets if a collision is detected, as can occur in the case of a multiple-token error, and transmits a collision packet; on reception of such a collision packet, the ring is closed again and the station accesses the ring line, in competition with other stations, with the risk of collision, after a randomly determined waiting time interval has elapsed, in that, with the ring line being opened, it transmits an information packet with a terminating free token and, if this information packet is transmitted without any collisions, removes said packet from the ring again without the terminating token. In the event of token loss, each station which wishes to transmit and which detects this accesses the ring line in the same manner, in competition with other stations, with the risk of collision.

Description

Procedure for token error correction in a token ring

Telecommunication system For fast transmission of digital signals between frequently changing remote stations (subscriber stations), for example between Telecommunication terminals and / or data processing facilities in one Spatially relatively narrow areas are often also found as local networks (LAN) designated telecommunication systems application in which the associated subscriber stations Access to a common transmission medium in accordance with an access regulation to have. Such local area networks are usually classified according to the type of transmission medium, differentiated from one another according to their topology and the type of access method (Clark et al .: "An Introduction to Local Area Networks", Proc. IEEE 66 (1978) 11, 1497 ... 1517): Common transmission media in local area networks are two twisted ones Shielded (twisted pair) cables, coaxial cables or optical waveguides with cores; in topological terms, a distinction is made in principle between star-shaped systems, typically with central switching, and (non-directional) bus and (directional) Ring systems, both typically with distributed switching.

From the large number of access methods, only two are intended here Methods are mentioned (Leinweber: local networks (LAN) ", Signal + Draht 76 (1984) 7/8, 119 ... 124): As a typical bus access method, the so-called. CSMA / CD (Carrier Sense Multiple Access with Collision Detection) method should be mentioned: Before a station starts transmitting, it listens to the bus to see if it is already there a transfer process is taking place. If so, it will wait for it first End from; then the station in question begins to transmit, initially continuing "listens" until it is certain after a certain period of time (round trip delay time) is that all other stations could notice their sending. Did in the same way If another station starts transmitting at about the same time, both stations will detect a collision of their digital signals with those of the other station, whereupon they cancel their sending process after a random period of time to start over.

This is outlined below as a typical ring access method Token-Passing-Procedure called: A certain signal word ("token"), which the statement "free" or occupied "circulates constantly in the ring Station begins to send, it must recognize the ("free") token and put it in the "occupied" token (hereinafter also referred to as "Connector") to which you can then send the sending message to adds. The message that goes through the rest of the stations and can be copied there in whole or in part, but only from the through the associated address of the specific station is finally received, is after complete Passing through the ring is deleted again by the sending station, and at the same time the "occupied" token is converted back into the free "token.

However, the access methods are not adapted to a specific LAN topology bound; a ring network can also be operated as a so-called contention ring, in which the message packets transmitted in the ring only after they have passed through the whole Ring line when the respective transmitting station is reached again from the ring line be removed again and in which a station willing to send is initially in the ring line listens to see whether a transfer process is already taking place there, and if so waits with access to the ring line until it recognizes a token and the Access authorization is granted, to which she must first insert the token into a Connector converts and then a message packet by opening the loop or (also a series of message packets separated from one another by a connector).

sends out a token that concludes the (last) message packet, while when the ring line is free, the station willing to transmit is in a collision-prone one Competition with other stations takes access to the loop at least then, if they received a message packet that was sent out earlier and terminated with a token removed from the loop again (Tanenbaum: Computer Networks ", Prentice Hall, 1981, p.311).

However, to come back to the token passing system outlined above, so in such a system, also known as a single token ring, care must be taken among other things to bear that system errors such as those in the form of a duplication of the token or also occur in the form of a token loss, can be resolved.

For this purpose, it is known among the ring stations with equal rights a so-called monitor station, detached from it, for generating the token for the first time and to provide for intervention in the event of a fault that does not occur of a (free or occupied) token during one of the sum of the ring cycle time and determines the maximum message packet duration corresponding monitoring period and then the ring by sending out a sufficiently long sequence of spaces cleans and then sends out a free token; in the same way is the monitor station also active when a station that is currently sending a received message or if a busy token is not received during said Monitoring period, a malfunction was detected and the message transmission aborted without generating a free token (Bux et al: A LOCAL-AREA COMMUNICATION NETWORK BASED ON A RELIABLE TOKEN-RING SYSTEM ", IFIP TC-6 Symposium on Local Computer Networks, Florence 1982, pp. 69 ... 82; Spaniol: Concept and evaluation methods for local computer networks ", Informatik-Spektrum 5 (1982) 3, 152 ... 170).

With such a monitoring station, however, the principle of equality becomes all ring stations violated, which has the consequence that the functioning of the ring system Despite the principle of equal rights for all ring stations, ultimately from functioning depends on a higher-level and therefore central station.

The invention now has the task of providing a possibility of a Specify token debugging in a single token ring that has no involvement requires a monitor station that is superordinate to the other ring stations.

The invention relates to a method for token error recovery in one Token ring telecommunication system, in which with error-free operation a ("free" or "occupied") token is constantly circulating in the ring; This method is characterized according to the invention that each transmitting station, based on the the sender addresses of those arriving via the ring line and from the message packets removed from the ring line detects a possible collision or which receives a collision packet via the ring line indicating a collision, such a collision packet is aborted if the transmission of the message packet that is still in progress is interrupted sends out and when such a collision packet is received, the distance of incoming ones Packets terminated and after a waiting period in collision-prone competition to other stations accesses the loop by opening the loop a message packet or a series of each through a connector from each other separated message packets with a (last) message packet terminating Sends out tokens, with collision-free transmission of the (des) sent out Message package (s) this (s) by holding it open and closing it again removed from the ring line without the final token from the ring.

The invention has the advantage of the principle of equality of all ring stations, even when eliminating multiple token errors, and to be able to do without the involvement of a higher-level monitor station. In in the same way, a token loss can also be taken into account, according to further invention any station willing to send, which the non-occurrence of a ("free" - or occupied "-) tokens during one of the sum of the ring cycle time and the maximum message packet duration determines the corresponding monitoring period, in collision-prone Competition with other stations accesses the ring line by opening it the ring line a message packet or a series of each through one Connector separate message packets with one the (last) message packet sends out the final token, with collision-free transmission of the (des) Message packet (s) sent out message packet (s) this (s) by corresponding Keeping the loop open and closing it again without the final token from Ring removed again.

Further particularities of the invention will become apparent from the following detailed explanation of an embodiment of a single token ring telecommunication system according to the invention with reference to the drawings. 1 shows an exemplary embodiment such a single token ring system; 2 ff. Illustrate certain operating situations in such a telecommunication system.

The drawing FIG 1 shows schematically in an understanding of the Invention required scope a telecommunication system with a by a Ring line R given transmission medium to which a plurality of subscriber stations T has access. The subscriber stations T are for this purpose each by means of a connection device (Ring interface) J connected to the ring line R, the connection device J on the one hand, the ring line section leading to it constantly with the input E connects the relevant station T and on the other hand depending on the respective switching state a switch S either the ring line R at this point above an 1-bit delay element V closes or the ring line R interrupts and instead the output A of the relevant station T with the continuing ring section connects. Such a connector J normally holds the ring R over their switch S closed, so that from other stations T originating message packets be transmitted in the ring R; at the same time, the connection circuit J allows the its associated station T a wiretapping of the ring line R.

If the associated station T itself sends message packets, the ring switch S of the relevant connection circuit J is switched over, see above that the ring R is interrupted at this point; the ring remains interrupted until the packet (s) sent out has (have) completely traversed the ring R and thus no longer appears on the ring (e-r-appear).

In the event of an error, as usual in comparable cases, it must be ensured that that the ring remains closed or

is closed, which is not to be pursued further here, since this is not necessary to understand the invention.

Message packets sent from a station T like this is also indicated in Figure 1, the station output A bit-serial from a memory WS are fed forth, in which message packets pending for transmission are in a queue can form; Copies of the packages sent in each case remain in the queue memory for the time being or, as is also indicated in FIG. 1, in a separate one associated therewith Memory MS stored until it is certain that they have been transmitted without errors.

As can also be seen from FIG. 1, may each station T a with have the station input E connected receive buffer register PR, which for Intermediate storage of message packets that are received via the ring line R is used are, however, of all received packets only the packets, their recipient address matches the ring address of the station currently being viewed, not discarded will. In Figure 1 it is indicated that the recipient address of a message packet an address detector AD is connected to the receiving part of the buffer register PR, the wired or otherwise stored address of the relevant station T compares with the recipient address contained in the respective received message packet and only unlocks the output of the buffer register PR if they match.

Simultaneously with the recording of one at the station just viewed T incoming message packets in their buffer register PR is the relevant The message packet is also forwarded from the associated connection device J in the ring R, provided that the station you are looking at was not the sender of the package itself. Was the station T currently under consideration, on the other hand, is the sender of one in this station T just received packet, the packet is in the connection device J from the ring R, which it has just passed through completely, is removed again; this happens in that the connection device J with the help of its switch S the ring R Holds interrupted until all of the station T currently being viewed has been sent Message packets from the station T have been received again. To do this, how this is also indicated in FIG. 1, a packet comparator PV each in the buffer register PR received message packet with the earliest one sent and compare the message packet still stored in the memory MS in order to find it in the event of a match to delete; the memory MS is empty, - what if necessary also by one of the respective Up / down counter indicating memory content can be displayed, - so are all the message packets just sent out by the station T in question after completely passing through the ring R again removed from the ring R, and in the Connection device J, the switch S can close the ring R again.

However, before sending message packets through When a station T arrives, it must first recognize the ("free") token have received the access authorization. In FIG 1 it is indicated in this regard that at Willing of station T to send an input of an AND element OA is activated, the other input of which is connected to that part of the buffer register PR, which, if necessary, accepts a received token. Upon receipt of such a token the coincidence condition of the AND element OA is then fulfilled, with which the just considered Station T is authorized to access the ring line R.

To exercise the access authorization is in the station T first the (free ") token is converted into a connector (" occupied "token); indicated that a monostable flip-flop BK started from the AND element OA whose working time span may correspond to a bit time span and that for this period of time via an OR gate SO the ring switch S belonging to the station T. Switches connection device J and at the same time unlocks a connector bit generator CG, so that instead of the last bit of the - by the way so far above the ring switch S in the ring R transmitted - tokens transmit an inverted bit and so a connector is transmitted instead of the token.

Then the interruption caused by the ring switch S is maintained the ring line R a message packet - or a series of each through message packets that are separate from each other via a connector. In FIG 1 this is indicated that from the output of the monostable flip-flop BK over an OR gate ZO a bistable flip-flop SK is activated, which is from its output accordingly unlocked the output of the queue memory WS and at the same time via the NAND gate SO holds the ring switch S in its switching state, in which it connects the station exit A with the outgoing ring line section.

After the previously explained removal of the one just viewed Station T sent out message packets from the one completely traversed by them Ring R may finally put the "free" token back into ring R from station T can be entered. In FIG 1 it is indicated for this purpose that a corresponding input side Memory cells of the memory MS connected NAND gate TO possibly determines that the memory MS no longer contains a message packet, and thereupon an output signal releases, through which a monostable flip-flop TK is started, its working period may correspond to the circular cycle time LR and this for this period of time via the OR element SO the ring switch S belonging to the station T. Connection device J toggles or holds in the toggle state and at the same time one to the station exit A leading token generator TG unlocked, so that a generated by the token generator TG ("Free") token is fed into the ring R.

From further detailed explanations of the above Outlined basic mode of operation of the telecommunications system outlined in FIG. 1, as given by a station T when message packets are sent is, can be disregarded here, since this is not necessary for an understanding of the invention is; Rather, the invention is based on known working principles of a single token ring. After these principles are based on a with special circuits provided in each station T realized embodiment have been explained, it should be noted, however, that a realization of the so far per se known ring access protocol also with the help of provided in the stations Microprocessors is possible.

It is now assumed that in such a ring system as was outlined above in its mode of operation with fault-free operation, erroneously an error status "multiple token" has occurred in which more as a token circulates in the ring.

In such a case, all Stations T, which recognize and pick up such a token, on the ring line and start sending a message packet.

At this point, take a look at the drawings of FIG. 2 to FIG. 7 thrown, which is somewhat simplified in comparison to the illustration in FIG Representation of a ring system clarify certain operational situations, how they can arise in such a telecommunication system.

Here, FIG 2 shows how an individual sent by a station Ts Message packet Ps of - based on the ring cycle time - of medium length in one occupies the ring R at a certain moment.

The operating situation outlined in FIG. 2 can arise when the station Ts that is currently transmitting has previously waited to access the ring line R. until it had the ("free") token circulating in the ring alone - as sketched in FIG. 3 recognized and picked up.

In FIG. 4 and FIG. 5, two operating situations are now outlined, such as they can arise if token duplication occurs incorrectly is and then two stations willing to send Ts and Tt each one at about the same time Recognize and pick up free tokens and thus access ring line R: According to 4, the station Tt begins to send its package, while that of the station Ts package Ps that has already been completely sent is in ring R; Send according to FIG 5 Both stations Ts and Tt deliver their packets Ps, Pt practically at the same time.

Both transmission situations lead to a collision, regardless of whether - what about the location of the respective recipient and the respective package length - the packages from the intended recipients in whole, in part or at all cannot be received.

Likewise, the operating situations outlined in FIG. 6 and FIG. how it appears when three stations Ts, Tt, Tu are accessed at approximately the same time the ring R can result in collisions.

It should be noted here that a collision occurs when one Station (e.g. station Tt in FIG 4 to FIG 7), which is a packet (Pt in FIG 4 to FIG 7) has sent or is still sending, then one of them different packet (Ps in FIG 4 and FIG 5; Pu in FIG 6 and FIG 7) of another Sender (Ts in FIG 4 and FIG 5; Tu in FIG 6 and FIG 7) receives without her beforehand to have received my own package.

In the operating situations outlined in FIG. 4 and FIG each of the two simultaneously transmitting stations Ts and Tt based on the collision an at least partial comparison that includes at least the sender addresses the one arriving at her via the ring line R - and removed from the ring line - Message packets with corresponding copies of the previously sent message packets determine. In FIG 1 it is indicated that with the output of the packet comparator PV is connected to the blocking input of a blocking element KU, which is connected to two further inputs each via an OR element VOe, VOs with the two-sided inputs of the packet comparator PV is connected. The blocking element KU for is via the two OR elements VOe, VOs the coincidence case is prepared as soon as at both inputs of the packet comparator PV one package is pending at a time; if both packages do not match, see above the coincidence condition for the locking element KU is met.

As soon as a station recognizes that a collision has occurred, interrupts they send their parcels. In Figure 1 is indicated in this respect that when meeting the Coincidence condition for the blocking element KU from its output via an OR element KO the bistable flip-flop SK is reset, with which the output of the queue memory WS is blocked.

If exactly two stations are involved in a collision, then In this way, both stations necessarily recognize the collision of the sent packets. However, if three or more stations are involved in the collision, this is not the case absolutely the case, as FIG. 6 shows.

To counter this, every station that detects a collision sends a collision packet K (in FIG. 7), which differs from every other message packet as well as tokens and connectors, and holds by means of their ring switch S (in Figure 1) the ring R interrupted until they receive a collision packet and removed it from the ring. In Figure 1 it is indicated that at the same time with the Resetting the bistable flip-flop SK activates a bistable flip-flop KK so that the ring switch S continues to be in its toggle state via the NAND gate SO remains, and that a collision packet generator KG is also unlocked, so that via the output A of the relevant station T and its ring switch S a collision packet is fed into the ring R.

Such an operating situation for the two stations is shown in FIG Ts and Tt are sketched, which accordingly each have a collision packet Ks or Send out Kt.

In the operating situation outlined in FIG. 7, the station Tu has up to now not recognized that a collision has occurred; but one recognizes from the drawing 7 shows that the station Tu will soon receive the collision packet sent out by the station Ts Ks is received.

A station, as in the example of FIG 7, the station Tu, at least has a package wholly or partially on the ring, but has not yet had its own collision package had sent because it could not detect a collision, also breaks a transmission process that is still running as soon as it receives a collision packet. It then for its part forwards a collision packet to the next station in ring R. In the drawing FIG 1 is indicated in this regard that a collision packet detector with the buffer register PR KD is connected, which responds when receiving a collision packet and thereby a Emits an output signal which triggers the same processes via the OR element KO, as in the manner explained above also by an output signal of the blocking element KU are triggered. After such a transfer of a received collision packet the ring R is closed again by the station T concerned; in FIG 1 is this indicated that after a required for the collision word forwarding Period of time by an appropriately dimensioned, started by the collision packet detector KD Timing element KL, the bistable flip-flop KK is reset.

The station T in question already had a collision itself detected and accordingly already sent out a collision packet, so If a collision packet is received, it is only removed from ring R, whereupon the ring is closed again by means of the associated ring switch and thus the Incoming packet removal is terminated. In FIG 1 it is indicated for this purpose that in such an operating situation the coincidence condition for an AND element KKU is met, one input of which is connected to the output via a bistable flip-flop KS of the blocking element KU is connected and the output side also to the reset input of the bistable flip-flop KK leads.

For the sake of completeness, it should be noted that in all stations, in which the ring R (in Figure 1) closed via the respective associated ring switch is, a collision packet is retransmitted unchanged like any other packet.

Each station affected by a collision reaches for a random one Waiting period in collision-prone competition with other stations on the Ring line R by opening the ring line R by sending a message packet or a series of message packets separated from one another by a connector sends out with a token that concludes the (last) message packet. For this the respective station can e.g. with the help of a random number generator, a from a pulse generator with a pulse period corresponding to the ring cycle time with counting pulses applied pulse counter and a random number and counter reading comparing comparators or with the help of a microprocessor implemented, randomly determined in length waiting time loop VS, after which Via the OR gate ZO (in FIG. 1) of the relevant station T (in FIG. 1) again the bistable flip-flop SK is activated, so that the station in question T again in in a manner corresponding to the processes already explained above with the transmission of the message packet begins.

The waiting period w is expediently dependent on this determined by the number z of collisions that the first packet of a sequence of from the station in question sent packets that were at the time of the collision detection was on the ring, has already learned about. This collision number z can, like this is also indicated in FIG. 1, determined with the aid of a collision counter KZ which is acted upon by the OR element KO with counting pulses and the respectively is reset to zero by the output of the packet comparator PV. The waiting period w is then expediently with (v for z <lb N w = ((2L R for z Wlb N measured, where LR is the cycle time, i is the serial number (position) of the currently considered Station in the ring and N is the number of stations in the ring and where v is a random variable is, the uniformly distributed values from the value interval 0, 22 2Z LR | accepts.

As long as one of the station you are currently viewing (possibly

again) the packet to be sent experienced fewer than lb N collisions has, i.e. the counter KZ shows a smaller collision number z, the waiting time becomes determined equally distributed from the interval 10, 2Z LR1. With a larger number of packages z is one of its serial numbers (position) in ring R for the station concerned corresponding fixed waiting period assigned to the product of the station number i and twice the ring cycle time LR. Aue this way is achieved that the waiting period is not even when unfavorable circumstances coincide can be any size.

The (last) message packet is concluded by a ("free") token, this in a manner corresponding to the generation process already explained above can be generated without having to go into it again here.

In the case of collision-free transmission, each station T sent message packet after passing through the ring R at this very station T removed from the ring again by means of her ring switch R which interrupts the ring R, but without the final ("free") token; rather, it remains in the ring. This is done by closing the ring R again by means of the ring switch S reached, whereby by timely switching back the ring switch S that already generated tokens remain in the ring R or such a token under renewed Switch of the ring switch S can be generated again in the manner described. A token is now circulating in ring R again; the multiple token error is thus resolved.

In one of the procedures of a remedy explained above Corresponding to multiple token errors, a token loss can also be corrected be by each station willing to send T (in Figure 1), the non-occurrence of a ("Free" - or "Occupied" -) tokens during one of the sum of the ring cycle time and the maximum Message packet length determines the corresponding monitoring period in collision-prone Competition with other stations on the ring line R accesses.

In FIG 1 it is indicated for this purpose that a possibly received Token-receiving part of the buffer register PR is connected to a token detector TD is the output signal indicating this on receipt of a ("free" or "occupied") token releases and which is followed by a monostable flip-flop VK, which by each Output signal of the token detector TD are started again and then for a certain, the sum of the ring cycle time and the maximum message packet duration corresponding period of time may remain in his working state.

If the monostable flip-flop VK is in its rest state, i.e. is no free or occupied token occurred within the specified (monitoring) period, so the station T willing to transmit intervenes in collision-prone competition with others about stations willing to send to the ring line R by opening the Ring line a message packet or a series of each through a connector separate message packets with one the (last) message packet final Sends out token. In FIG. 1 it is indicated in this regard that for this purpose the monostable flip-flop element VK again the bistable flip-flop SK is activated via the OR element ZO, so that the relevant station T in one of the processes already explained above starts sending the message packet accordingly. Is completed this message packet transmission in turn, corresponding to those already explained Operations, by a "free" token, which is used in the case of collision-free message packet transmission finally again, in accordance with the processes already explained, in ring R. remains. This means that a token is circulating in the ring again, with which the Token loss bug is fixed.

After in the above the invention using an exemplary embodiment was explained, that with special circuits provided in each station T. is realized, it should finally be noted that there is also a realization is possible with the help of microprocessors provided in the stations.

Claims (3)

Claims method for token troubleshooting in a token ring telecommunication system, in which one ("free" - or occupied "-) token is always present in case of error-free operation circulates in the ring, characterized in that each transmitting station (T) based on the sender addresses of the ones arriving via the ring line (R) and at the same time message packets removed from the ring line (R) detects a possible collision or via the ring line (R) a collision packet indicating a collision receives, with the interruption of the still ongoing message packet transmission such Sends a collision packet and, on receipt of such a collision packet, the distance incoming packets terminated and after a waiting period in collision-prone Competition with other stations (T) accesses the ring line (R) by by opening the ring line (R) a message packet or a series of each message packets separated from each other by a connector with the (last) Message packet sends out the final token, whereby it is collision-free Transmission of the sent out message packet (s) this (s) by appropriate Keeping the ring line (R) open and closing it again without the final token (To) removed from the ring again. 2. Procedure for token troubleshooting in a token ring telecommunications system, in which, with error-free operation, a ("free" or occupied) token is constantly in the Ring circulates, in particular according to claim 1, d u r ch g e k e n n n z e i c n e t that every station (T) willing to send, which does not occur one ("Free" - or "Occupied" -) tokens during one of the sum of the ring cycle time and the maximum Message packet length determines the corresponding monitoring period in collision-prone Competition with other stations (T) accesses the ring line (R) by by opening the ring line (R) a message packet or a series of each message packets separated from each other by a connector with the (last) Sends out the final token of the message packet, whereby it is collision-free Transmission of the sent out message packet (s) this (s) by appropriate Keeping the ring line (R) open and closing it again without the final token (To) removed from the ring again. 3. Telecommunication system according to claim 1, characterized in that that the waiting period w is measured with (v for z <lb N W = ((2LRi for z # 1b N is where LR is the cycle time, i is the serial number of the station in the ring and N are the number of stations in the ring and where v is an evenly distributed value the value interval | 0,2z LR | assuming random variable.